In a cylindrical alkaline dry cell such as LR6 or LR03, an alkaline power generation element including a cathode mixture, a separator, and an anode mixture is contained in a cylindrical metallic cathode can with a closed bottom, and an opening of the cathode can is sealed in an airtight manner by using a resin gasket, as disclosed in Patent document 1 for example.
The power generation element in which the tubular separator impregnated with an alkaline electrolyte is placed inside of the tubular-molded cathode mixture, and the gelled anode mixture is filled inside of the separator. The cathode can serves as a cell case, and also as a cathode current collector and a cathode terminal by directly contacting the cathode mixture. A metallic anode current collector in a bar shape is inserted into the anode mixture. This anode current collector is fixed by welding upright at an internal surface of a dish-shaped metallic anode terminal plate. The anode terminal plate, the anode current collector, and the sealing gasket are preassembled together, and configure a sealing unit that closes an opening of the cathode can.
The sealing gasket is a single-piece molded member of a polyamide resin, i.e. a nylon resin, and is formed by injection molding. The gasket includes a central boss portion, a peripheral packing portion and a middle barrier-wall portion, all of which are concentrically formed. Thin wall parts are partially formed in the gasket so that safety valve and stress-absorbing functions are provided. A through-hole through which the anode current collector is press-fittedly inserted is formed in the central boss portion.
Conventionally, a 6-6 nylon resin is used as the polyamide resin for the above-mentioned sealing gasket. However, in order to further improve durability and anti-leakage performance of the alkaline dry cell in a hot and humidity condition, the sealing gasket made of the polyhexamethylene dodecanamide resin, so-called the 6-12 nylon resin, is being developed as disclosed in Patent Document 2.
With such sealing gasket made of the 6-12 nylon resin, as described in Patent Document 2, it is possible to certainly improve the reliability of the safety valve operation and the anti-leakage performance in the alkaline dry cell using a sealing structure with a small number of parts and a low cost.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. H11-250875    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2005-79021